Ion removal system

ABSTRACT

An ion removal system includes: an ion removal device including a hard water storage configured to store hard water and a fine bubble generator configured to generate a fine bubble to supply the hard water storage with the fine bubble, for removing a metal ion from the hard water by adsorbing the metal ion in the hard water to the fines bubble in the hard water storage and crystallizing and precipitating the adsorbed metal ion; and a particle feeder configured to bring a particle containing a same element as that of the metal ion into the hard water at a feeding point, the feeding point being located upstream of the hard water storage or located in the hard water storage.

TECHNICAL FIELD

The present invention relates to an ion removal system.

BACKGROUND ART

Conventionally, there have been disclosed ion removal systems forremoving metal ion in hard water (e.g., see Patent Document 1).

The ion removal system in Patent Document 1 is intended to remove metalion (calcium ion and magnesium ion) in hard water using an ion exchangeresin. Specifically, the metal ion is removed from hard water in such away that the metal ion in the hard water is replaced with sodium ion bymaking the hard water flow through a treatment tank containing an ionexchange resin having a surface attached with the sodium ion. Thereby, ahardness of the hard water is reduced to produce soft water. The metalion present which have been contained in the hard water are captured onthe surface of the ion exchange resin.

PRIOR ART DOCUMENTS Patent Document

-   Patent Document 1: Japanese Patent Laid-Open Publication No.    2000-140840

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, the ion removal system in Patent Document 1 requires a largeamount of salt water for regenerating the ion exchange resin which hascaptured the metal ion, so that there is a problem of troublesomemaintenance. In addition, there is also the problem that thereproduction treatment causes reproduction waste water containing alarge amount of salt water, resulting in increases in soil pollution andburden of sewage treatment. Furthermore, the treated water softened bythe ion removal device has a high concentration of sodium ion, and maynot be recommended as drinking water in certain areas.

As described above, the ion removal system using the ion exchange resinhad a room for improvement from the viewpoints of maintainability andenvironmental property.

Therefore, an object of the present invention is to solve theaforementioned problems, and to provide an ion removal system havingbetter maintainability and environmental property.

Means for Solving the Problems

In order to achieve the above-mentioned object, an ion removal systemaccording to the present invention includes: a hard water storageconfigured to store hard water and a fine bubble generator configured togenerate a fine bubble to supply the hard water storage with the finebubble, for removing a metal ion from the hard water by adsorbing themetal ion in the hard water to the fines bubble in the hard waterstorage and crystallizing and precipitating the adsorbed metal ion; anda particle feeder configured to bring a particle containing a sameelement as that of the metal ion into the hard water at a feeding point,the feeding point being located upstream of the hard water storage orlocated in the hard water storage.

Effects of the Invention

According to the present invention, an ion removal system has bettermaintainability and environmental property.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of an ion removal device according toembodiment 1.

FIG. 2 shows a schematic view for explaining a hypothetical principle ofmetal ion adsorption with the ion removal device according to embodiment1.

FIG. 3 shows a schematic view for explaining a hypothetical principle ofmetal ion crystallization with the ion removal device according toembodiment 1.

FIG. 4 shows a schematic view for explaining a hypothetical principle ofreproduction treatment with the ion removal device according toembodiment 1.

FIG. 5A is a view showing a schematic configuration of a device used inexperimental example 1, showing a state after a predetermined time haselapsed since generation of fine bubble.

FIG. 5B is a view showing the schematic configuration of the device usedin experimental example 1, showing a state after a predetermined timehas further elapsed since the state shown in FIG. 5A.

FIG. 6 is a graph showing results of experimental example 1.

FIG. 7 is a schematic view for explaining a hypothetical principle ofmetal ion adsorption with an ion removal device according to embodiment2.

FIG. 8 is a schematic view for explaining a hypothetical principle ofmetal ion crystallization with the ion removal device according toembodiment 2.

FIG. 9 is a schematic view for explaining a hypothetical principle ofmetal ion adsorption with an ion removal device according to embodiment3.

FIG. 10 is a schematic view for explaining a hypothetical principle ofmetal ion adsorption and crystallization with the ion removal deviceaccording to embodiment 3.

FIG. 11 is a view showing a schematic configuration of a device used inexperimental examples 2 to 4.

FIG. 12 is a view showing a state of metal components crystallized inhard water.

FIG. 13A is a graph showing results of experimental example 2, showingthe relationship between the mixing ratio of ammonia and thecrystallization ratio of sample water.

FIG. 13B is a graph showing results of experimental example 2, showingthe relationship between the pH of sample water and the crystallizationratio of the sample water.

FIG. 14A is a graph showing results of experimental example 3, showingthe relationship between the operating time of a pump and thecrystallization ratio of sample water.

FIG. 14B is a graph showing results of experimental example 3, showingthe relationship between the operating time of the pump and the Cahardness of the sample water.

FIG. 14C is a graph showing results of experimental example 3, showingthe relationship between the operating time of the pump and the pH ofthe sample water.

FIG. 15A is a graph showing results of experimental example 4, showingthe relationship between the operating time of a pump and thecrystallization ratio of sample water.

FIG. 15B is a graph showing results of experimental example 4, showingthe relationship between the operating time of the pump and the Cahardness of the sample water.

FIG. 15C is a graph showing results of experimental example 4, showingthe relationship between the operating time of the pump and the pH ofthe sample water.

FIG. 15D is a graph showing results of experimental example 4, showingthe relationship between the operating time of the pump and the Cahardness and total carbonic acid concentration of the sample water.

FIG. 16 is a graph showing results of experimental example 5, showingthe relationship between the type of water and the height of a formextending from the water surface of evaluation water.

FIG. 17A is a graph showing results of experimental example 6, showingthe relationship between time and the crystallization ratio of Cahardness.

FIG. 17B is a graph showing results of experimental example 6, showingthe relationship between time and the crystallization ratio of totalhardness.

FIG. 18 is a schematic view of an ion removal device according to avariation of embodiment 1.

MODES FOR CARRYING OUT THE INVENTION

As a result of intensive investigations, the present inventors havefound a new finding that removal of the metal ion can be enhanced byusing “fine bubble” which has never been used in ion removaltechnologies for removing metal ion from hard water (water-softeningtechnologies), and this finding has led to the following invention.

Hereinafter, embodiments 1 to 3 according to the present invention willbe explained in detail with reference to the drawings.

Embodiment 1

FIG. 1 is a view showing a schematic configuration of an ion removalsystem 1 according to embodiment 1.

<Overall Configuration>

The ion removal system 1 according to embodiment 1 includes a primaryflow path 2, an ion removal device 3, a separation device 4, and asecondary flow path 5.

The primary flow path 2 is connected to the ion removal device 3. Theprimary flow path 2 is a flow path for supplying hard water to the ionremoval device 3. In embodiment 1, a pump P is provided in a connectionpoint between the primary flow path 2 and the ion removal device 3. Thepump P has a function to introduce the hard water flowing through theprimary flow path 2 to the separation device 4 through the ion removaldevice 3. The pump P is controlled by a control unit 6.

The ion removal device 3 includes a hard water storage 3A configured tostore hard water, and a fine bubble generator 3B configured to generatea fine bubble to be supplied to the hard water storage 3A. The ionremoval device 3 is configured to adsorb a metal ion in hard water inthe hard water storage 3A to the fine bubble to remove the metal ionfrom the hard water. The fine bubble generator 3B is disposed downstreamof the pump P in the flow direction of the hard water so that gas doesnot enter the pump P.

In embodiment 1, the metal ion is calcium ion (Ca²⁺) or magnesium ion(Mg²⁺). Furthermore, in embodiment 1, the fine bubble refers to a bubblehaving a diameter of 100 μm or less. The fine bubble include amicro-bubble (having a diameter of e.g., 1 to 100 μm) and a nano-bubble(having a diameter of e.g., less than 1 μm). The microbubble may be abubble that can be recognized by those skilled in the field of watertreatment as having a bubble diameter of micro order. The nano-bubblemay be a bubble that can be recognized by those skilled in the field ofwater treatment as having a bubble diameter of nano order. The finebubble has different properties from normal bubbles in points of a longretention time in water, difficulty in combination with other bubblesdue to difficulty in increasing the diameter as a single bubble; atendency to chemically react due to a large contact area, and the like.

Incidentally, the fine bubble may include a small ratio of bubble havinga diameter of 100 μm or more (such as a milli-bubble). For example, abubble including 90% or more of bubble having a diameter of 100 μm orless may be defined as the fine bubble. In addition, a condition of 50%or more of bubble having a diameter of 60 μm or less, a condition of 5%or more of bubble having a diameter of 20 μm or less, and the like maybe added. When measuring the diameter of the bubble (that is “bubblediameter”), for example, hard water containing the fine bubble may bedirectly photographed with a high-speed camera to calculate the bubblediameter by a three-point method in image processing. Alternatively, thebubble diameter may be measured by any other method. A timing ofmeasuring the bubble diameter may be optionally selected as long as thefine bubble remains in the hard water storage. One example of theconditions for the aforementioned measuring method using a high-speedcamera is as follows.

High-speed camera: FASTCAM 1024 PCI (PHOTRON LIMITED)

Lens system: Z16 APO (Leica Microsystems)

Objective lens: Planapo 2.0× (Leica Microsystems)

Shooting speed: 1000 fps

Shutter speed: 1/505000 sec

Image area: 1024×1024 pixel (microbubble shooting area 1.42 mm×1.42 mm,milli-bubble shooting area 5.69 mm×5.69 mm)

Image processing software: Image-Pro Plus (Media Cybermetics, Inc.)

In embodiment 1, an ion removal gas supplier 7 and a dissolving agentsupplier 8 are connected to the fine bubble generator 3B via a gasswitching mechanism 9.

The ion removal gas supplier 7 is configured to supply the fine bubblegenerator 3B with an ion removal gas for removing the metal ion in thehard water. The ion removal gas supplier 7 is, for example, an air pumpfor supplying gas. In embodiment 1, the ion removal gas supplier 7 isconfigured to supply “air” as the ion removal gas to the fine bubblegenerator 3B. The ion removal gas supplier 7 and the gas switchingmechanism 9 are connected by an ion removal gas flow path 120.

In embodiment 1, an ion removal gas storage 100 is connected to the ionremoval gas supplier 7. The ion removal gas storage 100 is configured tostore the ion removal gas to be supplied to the ion removal gas supplier7. The ion removal gas storage 100 is, for example, a gas storage tankor a high-pressure gas cylinder. The ion removal gas supplier 7 suppliesthe fine bubble generator 3B with the ion removal gas supplied from theion removal gas storage 100.

In embodiment 1, the ion removal gas storage 100 is configuredintegrally with a particle storage 106 of a particle feeder 102described later.

The ion removal gas supplier 7 is not limited to such a configuration,and may be a device in which the ion removal gas supplier 7 itselfgenerates the ion removal gas.

The dissolving agent supplier 8 is configured to supply the fine bubblegenerator 3B with a dissolving gas, which is one example of a dissolvingagent for dissolving a crystal of metal component precipitated as themetal ion removed from the hard water is crystallized. The dissolvingagent supplier 8 and the gas switching mechanism 9 are connected by adissolving agent flow path 122. In embodiment 1, the dissolving agentsupplier 8 is configured to supply the fine bubble generator 3B with“carbon dioxide (CO₂)” as the dissolving gas. The dissolving agentsupplier 8 is disposed upstream of the separation device 4 in the flowdirection of the hard water so that the dissolving agent can be suppliedto the separation device 4. The dissolving agent supplier 8 may include,for example, a tank filled with the dissolving agent. Alternatively, thedissolving agent supplier 8 may be a device configured to generate thedissolving agent. Furthermore, the dissolving agent supplier 8 may be adevice to be connected to a dissolving agent supply source.

The gas switching mechanism 9 is a mechanism configured to performswitching so that either the ion removal gas or the dissolving gas issupplied to the fine bubble generator 3B. Switching by the gas switchingmechanism 9 selectively performs a water-softening treatment with theion removal gas or a reproduction treatment with the dissolving gas. Thegas switching mechanism 9 is includes, for example, one or more valves.A switching operation of the gas switching mechanism 9 is controlled bythe control unit 6.

When the gas switching mechanism 9 is switched to supply the ion removalgas, the fine bubble generator 3B generates a fine bubble containing theion removal gas. Then, the fine bubble removes the metal ion andseparates a crystal of metal component from the hard water, therebysoftening the hard water. A principle of the water-softening treatmentwill be explained in detail later.

On the other hand, when the gas switching mechanism 9 is switched tosupply the dissolving gas, the fine bubble generator 3B generates a finebubble containing the dissolving gas. Then, the fine bubble performsreproduction of the separation device 4 by causing a crystal of metalcomponent adhering to the separation device 4 to dissolve, as describedlater. A principle of the reproduction treatment will be explained indetail later.

The separation device 4 is connected to the ion removal device 3 via aconnection flow path 3C provided at an upper outer peripheral of thehard water storage 3A. The separation device 4 is a device configured toseparate the crystal of metal component precipitated as the metal ionremoved from the hard water by the ion removal device 3 is crystallized.The ion removal device 3 and the separation device 4 can reduce aconcentration (hardness) of the metal ion in the hard water to apredetermined concentration or less, thereby producing soft water. Asthe definitions of hard water and soft water, for example, the WHOdefinition may be used. That is, water having a hardness of less than120 mg/L may be defined as soft water, and water having a hardness of120 mg/L or more may be defined as hard water.

In embodiment 1, the separation device 4, having a tapered innerperipheral surface 4Aa whose diameter decreases as going down, is acyclone-type centrifugal separator, where the hard water flows downwardin spiral along the inner peripheral surface 4Aa to separate the crystalof metal component. In embodiment 1, the separation device 4 includes aseparation section 4A having the inner peripheral surface 4Aa, and acrystal storage 4B configured to store the crystal of metal component.

The connection flow path 3C is connected to the separation section 4A soas to discharge the water that has passed through the ion removal device3, in a direction eccentric from a central axis of the separationsection 4A. Such an eccentric arrangement causes the water dischargedinto the separation section 4A to flow downward in spiral along theinner peripheral surface 4Aa. Metal ion having a large specific gravityremoved from the hard water moves toward the inner peripheral surface4Aa by centrifugal separation and then precipitates as the crystal ofmetal component in the vicinity of the inner peripheral surface 4Aa.Some of the crystal adhere to the inner peripheral surface 4Aa.

The crystal storage 4B is disposed below the separation section 4A. Thecrystal storage 4B includes a discharge flow path 4Ba configured todischarge water containing the crystal of metal component. The dischargeflow path 4Ba is provided with an opening/closing valve 10 capable ofopening and closing the discharge flow path 4Ba. An opening/closingoperation of the opening/closing valve 10 is controlled by the controlunit 6. A discharging-side backflow prevention mechanism 11 is provideddownstream of the discharge flow path 4Ba of the opening/closing valve10 in the discharge direction.

The discharging-side backflow prevention mechanism 11 is a mechanismconfigured to prevent the crystal of metal component from flowing backinto the separation device 4. The discharging-side backflow preventionmechanism 11 can suppress the crystal of metal component from beingmixed again into the treated water (that is, “soft water”) obtained bythe separation of the crystal of metal component from the hard water.The discharging-side backflow prevention mechanism 11 includes, forexample, one or more check valves. Alternatively, the discharging-sidebackflow prevention mechanism 11 may be includes, for example, a vacuumbreaker. Furthermore, the discharging-side backflow prevention mechanism11 may be configured to provide a spout space at an outlet of thedischarge flow path 4Ba in order to prevent backflow.

The secondary flow path 5 is connected to the separation device 4. Thesecondary flow path 5 is a flow path for taking out the treated water,in which the crystal of metal component has been separated, from theseparation device 4. In embodiment 1, since the separation device 4 is acyclone-type centrifugal separator, the crystal of metal component canbe collected in the vicinity of the inner peripheral surface 4Aa. Inorder to suppress the crystal of metal component from entering thesecondary flow path 5, the secondary flow path 5 is connected to anupper central position of the separation section 4A away from the innerperipheral surface 4Aa.

The treated water flowing through the secondary flow path 5 is suppliedto, for example, a kitchen, a bathroom, a toilet, a washbasin, and thelike. When a flow rate of the liquid from the primary flow path 2 to thesecondary flow path 5 is drastically reduced by use of the treatedwater, a centrifuge separation speed of the metal ion from the hardwater may be decreased, leading to a decreased removing efficiency ofthe metal ion. Also, the crystal of metal component may be mixed intothe treated water.

Therefore, in embodiment 1, a return flow path 12 is connected betweenthe separation device 4 and the primary flow path 2, which returns tothe primary flow path 2 some of the treated water in which the crystalof metal component has been separated from the hard water by theseparation device 4. That is, a circulation flow path is constituted bythe primary flow path 2, the ion removal device 3, the separation device4, and the return flow path 12. With this circulation flow path,fluctuations in the flow rate of the liquid flowing from the primaryflow path 2 to the secondary flow path 5 can be further stabilized,suppressing a decreased removing efficiency of the metal ion.Furthermore, driving the pump P to forcibly circulate the liquid in thecirculation flow path can further stabilize the fluctuations in the flowrate of the liquid, further suppressing the decreased removingefficiency of the metal ion. Furthermore, the crystal of metal componentcan be suppressed from being mixed into the treated water.

It is preferable that the flow rate of the liquid flowing through thecirculation flow path is equal to or higher than the flow rate of thesoft water to be used (e.g., 2 L/min). As the flow rate of the liquidflowing through the circulation flow path is higher than the flow rateof the soft water to be used, the fluctuations in the flow rate of theliquid can be more stabilized, thereby producing soft water stably.Furthermore, it is preferable that the circulation flow path is a closedsystem. Thereby, air is suppressed from entering the circulation flowpath, and thus the fluctuations in the flow rate of the liquid can befurther stabilized.

In embodiment 1, one end 12 a of the return flow path 12 is openedtoward the central axis of the separation section 4A. Thereby, thecrystal of metal component, which have precipitated in the vicinity ofthe inner peripheral surface 4Aa, is suppressed from entering the returnflow path 12. Furthermore, the connection flow path 3C of the ionremoval device 3 is connected to the separation section 4A below the oneend 12 a of the return flow path 12. That is, the one end 12 a of thereturn flow path 12 is located above the outlet of the connection flowpath 3C from which the hard water in which the metal ion have beenremoved is discharged downward in a spiral shape. This arrangementfurther suppresses the crystal of metal component, which haveprecipitated in the vicinity of the inner peripheral surface 4Aa,entering the return flow path 12.

A supply-side backflow prevention mechanism 13 is provided in theprimary flow path 2. The supply-side backflow prevention mechanism 13 isa mechanism configured to prevent the fine bubble and the treated waterfrom flowing back to the supply side of the hard water. The supply-sidebackflow prevention mechanism 13 includes, for example, one or morecheck valves. In embodiment 1, the supply-side backflow preventionmechanism 13 is provided upstream of the return flow path 12 in the flowdirection of the hard water flowing in the primary flow path 2. Thereby,the fine bubble, the treated water, and the like can be more reliablyprevented from flowing back to the supply-side of the hard water.

Furthermore, when maintenance is required, for example, due to a failureof the ion removal device 3 or the like, water cannot be used during themaintenance. Therefore, in embodiment 1, the primary flow path 2 and thesecondary flow path 5 are connected with each other by a bypass flowpath 14. The ion removal system 1 also includes a flow switchingmechanism configured to switch the flow direction of the hard waterflowing through the primary flow path 2 to either the ion removal device3 or the bypass flow path 14. Switching by the flow switching mechanismcan cause the hard water flowing through the primary flow path 2 to flowto the secondary flow path 5 through the bypass flow path 14, so thatthe hard water can be used even during maintenance. In addition,switching by the flow switching mechanism enables the hard water and thetreated water (soft water) to be selectively used, not even duringmaintenance.

In embodiment 1, the flow switching mechanism includes a first valve 15Acapable of opening and closing the primary flow path 2, a second valve15B capable of opening and closing the secondary flow path 5, and athird valve 15C capable of opening and closing the bypass flow path 14.Opening/closing operations of the first valve 15A, the second valve 15B,and the third valve 15C are controlled by the control unit 6.

The control unit 6 is configured to selectively execute first control toopen the first valve 15A and the second valve 15B while closing thethird valve 15C, or second control to close the first valve 15A and thesecond valve 15B while opening the third valve 15C. When the controlunit 6 executes the first control, the hard water flowing through theprimary flow path 2 goes to the ion removal device 3 to be softened andthen goes into the secondary flow path 5. Thereby, the treated water(soft water) is discharged from the outlet of the secondary flow path 5.When the control unit 6 executes the second control, the hard waterflowing through the primary flow path 2 goes to the secondary flow path5 through the bypass flow path 14. Thereby, the hard water is dischargedfrom the outlet of the secondary flow path 5. That is, executing thefirst control or the second control by the control unit 6 enablesselective discharging of the hard water or the treated water (that is,soft water) from the outlet of the secondary flow path 5.

In embodiment 1, a particle feeder 102 is further provided. The particlefeeder 102 is a device configured to bring a particle containing thesame element as that of the metal ion into the hard water. The particlefeeder 102 in embodiment 1 brings a particle of CaCO₃ (that is, calciumcarbonate) containing Ca that is the same element as Ca²⁺ (that is,calcium ion) of the metal ion. Bringing the particle of CaCO₃ into thehard water promotes the reaction of crystallizing Ca²⁺ and precipitatingthem as CaCO₃ as described later.

The particle feeder 102 of embodiment 1 includes a particle feedingmechanism 104 and a particle storage 106. The particle feeding mechanism104 has a mechanism configured to bring the particle described aboveinto the hard water. An example of the particle feeding mechanism 104includes an extruder and a particle-containing soluble agent (that is, asolid material that contains a particle and is soluble in water). Inparticular, the particle feeding mechanism 104 of embodiment 1 pushesout a gel particle to be brought into the hard water. The particlestorage 106 is a member configured to store the particle to be suppliedto the particle feeding mechanism 104. The particle storage 106 is, forexample, a particle storage tank.

The particle feeder 102 includes a first flow path 108, a second flowpath 110, and a third flow path 112. The first flow path 108 is a flowpath to connect the particle feeding mechanism 104 to the ion removalgas flow path 120. The second flow path 110 is a flow path to connectthe particle feeding mechanism 104 to the primary flow path 2. The thirdflow path 112 is a flow path to connect the particle feeding mechanism104 to the hard water storage 3A.

The particle feeder 102 is controlled by the control unit 6 so as tobring particle into the hard water via any one of the first flow path108, the second flow path 110, and the third flow path 112.

When the first flow path 108 is selected, the particle is brought intothe ion removal gas flow path 120. Then, a first feeding point 108Aexists in the ion removal gas flow path 120. When the second flow path110 is selected, the particle is brought into the primary flow path 2.Then, a second feeding point 110A exists in the primary flow path 2.When the third flow path 112 is selected, the particle is brought intothe hard water storage 3A. Then, a third feeding point 112A exists inthe hard water storage 3A.

<Water-Softening Treatment>

Next, a principle of a water-softening treatment using a fine bubblewill be explained in more detail.

It is predicted that once a fine bubble containing air is supplied intohard water, actions as described in the following sections (1) and (2)are caused on the metal ion in the hard water. Specifically, it ispredicted that the crystal of metal component can be removed from thehard water by adsorbing the metal ion in the hard water to the finebubble and crystallizing the adsorbed metal ion. More specifically, theprocess is as follows. Note that the present invention is notnecessarily restricted to the specific principle described in thefollowing sections (1) and (2).

(1) Metal Ion Adsorption

As shown in FIG. 2, once the fine bubble containing air is supplied intothe hard water, H⁺ (that is, hydrogen ion) and OH⁻ (that is, hydroxideion) are mixed on the surface of the fine bubble, in which H⁺ ispositively charged and OH is negatively charged (only OH⁻ is shown inFIG. 2). On the other hand, the hard water contains Ca²⁺ and Mg²⁺ aspositively charged metal ion. In the following explanation, Ca²⁺ will betaken as an example of the metal ion.

The positively charged Ca²⁺ is adsorbed to OH⁻ existing on the surfaceof the fine bubble by the intermolecular force action (that is,interionic interaction). In this manner, Ca²⁺ can be adsorbed to thefine bubble. Incidentally, although the surface of the fine bubble hasH⁺ which repels Ca²⁺, it is considered that OH⁻ acts more preferentiallythan H⁺ and adsorbs Ca²⁺. This “adsorption of metal ion” is mainlyperformed in the ion removal device 3.

(2) Crystallization of Metal Ion

In addition to the reaction shown in FIG. 2, the supply of the finebubble containing air into the hard water promotes the reaction shown inFIG. 3. Specifically, unlike normal bubbles, the fine bubble suppliedinto the hard water is difficult to rise up, and dissolves in the hardwater, and therefore gradually contracts by an increased surface tensionas shown in FIG. 3. As described above, Ca²⁺ is adsorbed to the surfaceof the fine bubble. More specifically, Ca²⁺ exists as a calcium ion of asoluble Ca(HCO₃)₂ (that is, calcium bicarbonate). Herein, as the finebubble gradually contracts, a concentration of the dissolved Ca²⁺ on thesurface of the fine bubble increases. Because of the increase in theconcentration of the dissolved Ca²⁺, the Ca²⁺ becomes supersaturated atsome point, and then crystallizes and precipitates. A specific chemicalequation representing this process is as the following equation 1.

Ca(HCO₃)₂→CaCO₃+CO₂+H₂O  (Equation 1)

Since CaCO₃ (that is, calcium carbonate) is insoluble (that is, waterinsoluble), CaCO₃ precipitates as a crystal of metal component. Thereby,the Ca²⁺ dissolved as Ca²⁺ of Ca(HCO₃)₂ precipitated as a crystal. Withsuch a reaction promoted, CaCO₃ precipitated as Ca²⁺ of a metal ion iscrystallized can be separated from the hard water. This “crystallizationof metal ion” is mainly performed in the separation section 4A of theseparation device 4.

Incidentally, although a reaction reverse to the equation 1 may alsooccur in the same water, it is predicted that by continuously supplyingthe fine bubble, the reaction in the direction of the equation 1preferentially occurs in the equilibrium relationship. Furthermore,since the reaction reverse to the equation 1 basically does not occurunless CO₂ gas is blown from the outside, it is considered that thereaction in the direction of the equation 1 preferentially occurs.

In embodiment 1, since the separation device 4 is a cyclone-typecentrifugal separator, the crystal of metal component precipitates inthe vicinity of the inner peripheral surface 4Aa of the separationsection 4A to be stored in the crystal storage 4B. The crystal of metalcomponent stored in the crystal storage 4B is discharged through thedischarge flow path 4Ba when the opening/closing valve 10 is opened.Separating the crystal of metal component from the hard water in thisway achieves softening of the hard water.

Furthermore, in embodiment 1, the particle of CaCO₃ is brought into thehard water by using the particle feeder 102. Specifically, the particleof CaCO₃ is brought through any one of the first flow path 108, thesecond flow path 110, the third flow path 112 by controlling theparticle feeder 102 with the control unit 6.

Bringing the particle of CaCO₃ containing Ca, which is the same elementas Ca²⁺ of the metal ion, leads to adsorption of the calcium ion tocrystal nuclei, thereby increasing the adsorption amount of the metalion. Therefore, the crystallization of the metal ion explained above canbe promoted. Also, when the particle of CaCO₃ is brought, a reaction, inwhich the Ca²⁺ ions and CO₃ ²⁻ ions dissolved in water are used for thegrowth of particle, only occurs, so that the crystallization can bepromoted.

When the first flow path 108 is used, the particle of CaCO₃ is broughtto the first feeding point 108A located in the ion removal gas flow path120. The particle of CaCO₃ is supplied to the fine bubble generator 3Bfrom the first feeding point 108A. In the fine bubble generator 3B, afine bubble is generated with the particle of CaCO₃. Therefore, theparticle of CaCO₃ can be supplied into the hard water in the state ofbeing mixed with the fine bubble. Thereby, the crystallization of themetal ion adsorbed to the fine bubble in the hard water storage 3A canbe further promoted.

When the second flow path 110 is used, the particle of CaCO₃ is broughtto the second feeding point 110A located in the primary flow path 2. Theparticle of CaCO₃ is supplied to the fine bubble generator 3B from thesecond feeding point 110A via the pump P. Similarly to the case of usingthe first flow path 108, the particle is supplied at an upstream pointof the fine bubble generator 3B, and thus a fine bubble can be generatedwith the fine bubble generator 3B including the particle. Therefore, thesame effects as in the case of using the first flow path 108 can beexhibited.

When the third flow path 112 is used, the particle of CaCO₃ is broughtto the third feeding point 112A located in the hard water storage 3A.Unlike the cases of using the first flow path 108 and the second flowpath 110, the particle of CaCO₃ is brought to the downstream point ofthe fine bubble generator 3B. With such a configuration, since theparticle of CaCO₃ is directly brought into the hard water storage 3A,the charge amount of the particle of CaCO₃ can be controlled by thecontrol unit 6, and thus the crystallization of the metal ion in thehard water storage 3A can be controlled precisely.

<Reproduction Treatment>

Next, a principle of a reproduction treatment using a fine bubble willbe explained in more detail.

By performing a water-softening treatment, some of CaCO₃ precipitated asthe metal ion is crystallized adhere to the inner peripheral surface 4Aaof the separation section 4A. As a treatment for returning this CaCO₃ toCa(HCO₃)₂, a reproduction treatment is performed. Specifically, the finebubble generator 3B generates a fine bubble containing carbon dioxide,which is a gas different from that used in the water-softeningtreatment.

As shown in FIG. 4, the following reaction is promoted by supplying finebubble of carbon dioxide to CaCO₃ adhering to the inner peripheralsurface 4Aa of the separation section 4A.

CaCO₃+CO₂+H₂O→Ca(HCO₃)₂  (Equation 2)

This reaction produces soluble (that is, water-soluble) Ca(HCO₃)₂ frominsoluble CaCO₃. Ca(HCO₃)₂ dissolves in water and moves to the crystalstorage 4B. Ca(HCO₃)₂ that has moved to the crystal storage 4B isdischarged through the discharge flow path 4Ba when the opening/closingvalve 10 is opened. Thereby, the insoluble CaCO₃ adhering to the innerperipheral surface 4Aa of the separation section 4A is discharged to theoutside, and the inner peripheral surface 4Aa can be returned to itsoriginal state. Thereafter, the aforementioned water-softening treatmentcan be performed again.

In the above description, although Ca²⁺ has been taken as an example ofthe metal ion, it is predicted that the same reaction occurs as forMg²⁺.

As described above, when a metal ion is removed from hard water by usingan ion exchange resin, a large amount of salt water is required toreproduce the ion exchange resin. On the other hand, according to theion removal system 1 of embodiment 1, the metal ion is removed from thehard water by using the fine bubble, so that a large amount of saltwater to be required for reproducing an ion exchange resin isunnecessary. Thereby, the reproduction treatment can be simplified, andmaintenance can be performed easily. Furthermore, since reproductionwaste water containing salt water is not caused, soil pollution and aburden on sewage treatment can be suppressed, and environmental propertycan be improved. Furthermore, the concentration of sodium ion in thetreated water does not increase, so that the generated treated water canbe used as drinking water.

Still furthermore, according to the ion removal system 1 of embodiment1, since air is used as the ion removal gas, the costs for generatingthe fine bubble can be reduced to an extremely low level.

Still furthermore, according to the ion removal system 1 of embodiment1, the reproduction treatment is performed by supplying the fine bubbleof carbon dioxide as the dissolving gas after the metal ion is removedfrom the hard water. Thereby, the reaction of producing solubleCa(HCO₃)₂ from insoluble CaCO₃ can be promoted, and thus thereproduction treatment can be promoted.

Still furthermore, according to the ion removal system 1 of embodiment1, the metal ion is Ca²⁺ and the particle is CaCO₃. Since Ca²⁺ becomesCaCO₃ when crystallized, the reaction of crystallizing Ca²⁺ in the hardwater can be improved by bringing CaCO₃ into the hard water in advance.

Still furthermore, according to the ion removal system 1 of embodiment1, the particle feeder 102 includes the particle feeding mechanism 104and the particle storage 106. With such a configuration, each of theparticle feeding mechanism 104 and the particle storage 106 can beconfigured in various modes, and therefore the degree of freedom indesigning the particle feeder 102 is improved. Still furthermore, inembodiment 1, the particle storage 106 and the ion removal gas storage100 are integrated with each other. With such a configuration, theparticle and the ion removal gas can be easily replenished, therebyimproving user convenience.

Still furthermore, according to the ion removal system 1 of embodiment1, the particle feeder 102 brings the gel particle. With such aconfiguration, the particle can be brought more easily to the feedingpoints than the case of using powder or the like.

Experimental Example 1

Next, experimental example 1 performed to confirm the principle ofwater-softening treatment by fine bubble will be explained. Here, anexperiment was conducted using a device 20 shown in FIGS. 5A and 5B.

FIGS. 5A and 5B present schematic configurations of the device 20 usedin Experimental example 1. FIG. 5A presents a state a predetermined timeafter generating fine bubble (specifically, after 15 seconds), and FIG.5B presents a state further a predetermined time after the state shownin FIG. 5A (specifically, after 45 seconds). The state of FIG. 5Acorresponds to a state 15 seconds after generating the fine bubble inFIG. 6, and the state of FIG. 5B corresponds to a state 60 seconds aftergenerating the fine bubble in FIG. 6.

The device 20 shown in FIGS. 5A and 5B refers to an experimental devicecapable of supplying fine bubble 23 from a bottom face side in a watertank 22 (hard water storage section) for storing a hard water 21. In thedevice 20, a concentration of the metal ions in the hard water 21 can bemeasured at two points, the bottom face side and the water surface side.The fine bubble 23 were supplied into the water tank 22 using thisdevice 20, and results of detecting transitions of the metal ionconcentrations at the bottom face side and the water surface side shownin FIG. 6 were obtained.

The results shown in FIG. 6 could demonstrate an effect of “metal ionadsorption by fine bubble” explained above. Specific results will bedescribed later.

As shown in FIGS. 5A and 5B, the device 20 includes the water tank 22, agas supply section 24, a first pipe 25, a fine bubble generation section26, a second pipe 27, a pump 28, and a first water intake section 30, asecond water intake section 32, and a metal ion concentration detector34.

The water tank 22 refers to a water tank for storing the hard water 21.In the example shown in FIGS. 5A and 5B, the water tank 22 is configuredso as to be a vertically long tank. The gas supply section 24 refers toa member for supplying a gas to the fine bubble generation section 26through the first pipe 25. The fine bubble generation section 26 refersto a device for generating the fine bubble 23 originating from the gassupplied from the gas supply section 24. The fine bubble generationsection 26 corresponds to the aforementioned fine bubble generator 3B.The gas is supplied from the gas supply section 24 to the fine bubblegeneration section 26 by a negative pressure effect of the pump 28through the second pipe 27.

The first water intake section 30 refers to a member for taking thesample water of the hard water 21 from a vicinity of a bottom face 22 aof the water tank 22. The second water intake section 32 refers to amember for taking the sample water from a vicinity of a water surface 22b of the water tank 22. Height positions of the first water intakesection 30 and the second water intake section 32 may be set to anyposition, and a distance D1 from the first water intake section 30 tothe second water intake section 32 can be adjusted to a desired value.

In the examples shown to FIGS. 5A and 5B, the height position of thefirst water intake section 30 is set to substantially the same positionas the height position where the fine bubble 23 are produced by the finebubble generation section 26.

The metal ion concentration detector 34 refers to a member for detectinga metal ion concentration in the sample water taken from the first waterintake section 30 and the second water intake section 32.

In the above configuration, once the fine bubble generation section 26and the pump 28 are operated, the gas is sent from the gas supplysection 24 to the fine bubble generation section 26 through the firstpipe 25 by the negative pressure effect of the pump 28 through thesecond pipe 27. The fine bubble generation section 26 generates the finebubble 23 using this gas as a raw material and supplies the gas to thewater tank 22 (arrow A1 in FIG. 5A).

The fine bubble 26 and the pump 28 are operated for a predeterminedperiod (15 seconds in embodiment 1) to continuously generate the finebubble 23.

Subsequently, the operation of the fine bubble 26 and the pump 28 isterminated. After terminating the operation, a predetermined idle periodis provided (45 seconds in embodiment 1).

As shown in FIG. 5A, at the end of the operation period (15 secondsafter generation of the fine bubble), it was visually confirmed that thefine bubble 23 supplied into the water tank 22 ascended in the hardwater 21 (arrow A2) and accumulated in a lower part of the water tank22.

As shown in FIG. 5B, at the end of the idle period (60 seconds aftergeneration of the fine bubble), it was visually confirmed that the finebubble 23 supplied into the hard water 21 further ascended, reached thewater surface 22 b (arrow A3), and accumulated in an upper part of thewater tank 22.

At a predetermined timing during the operation, the sample water wastaken out from the first water intake section 30 and the second waterintake section 32, and results of measuring the metal ion concentrationby the metal ion concentration detector 34 are shown in FIG. 6.

Specific experimental conditions regarding the results in FIG. 6 will bedescribed below.

(Experimental Condition)

Type of gas supplied by the gas supply section 24: air

Hardness of the hard water 21: about 300 mg/L

Temperature of the hard water 21: 25° C.

Distance D1 from the first water intake section 30 to the second waterintake section 32: about 1 m

Operation period of the fine bubble generation section 26 and the pump28: 15 seconds

Idle period of the fine bubble generation section 26 and the pump 28: 45seconds

Metal ion concentration detector 34: LAQUA F-70 manufactured by HORIBA,Ltd.

Metal ion to be measured: Ca²⁺

Timing for taking the sample water: 0 seconds, 15 seconds, 30 seconds,and 60 seconds after the start of the operation

In FIG. 6, the abscissa represents an elapsed time (seconds) fromgeneration of the fine bubble, and the ordinate represents aconcentration transition (%) of the metal ions (Ca²⁺) detected by themetal ion concentration detector 34. The metal ion concentrationtransition represents a metal ion concentration transition relative to100% of the metal ion concentration measured at the start of theoperation.

As shown in FIG. 6, after 15 seconds, a concentration of the samplewater extracted from the first water intake section 30 in the vicinityof the bottom face 22 a of the water tank 22 increases to about 108%.Afterward, the concentration gradually decreases at the idle period andfinally decreases to about 97%.

On the other hand, the concentration of the sample water extracted fromthe second water intake section 32 in the vicinity of the water surface22 b of the water tank 22 is retained at 100% until 15 seconds havepassed, then gradually increases at the subsequent idle period, andfinally incrementally increases to about 115%.

A result of associating the result of the metal ion concentrationtransition with the behavior of the fine bubble 23 is as below.

At the time when 15 seconds have passed, as shown in FIG. 5A, the metalion concentration increases in the sample water in the first waterintake section having the accumulating fine bubble 23. On the otherhand, the metal ion concentration is mostly unchanged in the samplewater in the second water intake section 32 having no accumulating finebubble 23.

At the time when 60 seconds have passed, as shown in FIG. 5B, the metalion concentration decreases to just under 100% in the sample water inthe first water intake section 30 having no accumulating fine bubble 23.On the other hand, the metal ion concentration remarkably increases inthe sample water in the second water intake section 32 having theaccumulating fine bubble 23.

According to such a result, it is predicted that Ca²⁺ as a metal ion inthe hard water 21 is adsorbed by the fine bubble 23 and ascends as thefine bubble 23 ascend.

Based on the above prediction, the effect of “metal ion adsorption byfine bubble” explained above could be demonstrated.

Embodiment 2

The ion removal system according to embodiment 2 of the presentinvention will be explained. Note that primarily points different fromthe points in embodiment 1 will be explained in embodiment 2. Inembodiment 2, the same or similar constituents as those in embodiment 1are described with the same reference numerals as in embodiment 1. Inembodiment 2, descriptions overlapping those in embodiment 1 areomitted.

Embodiment 2 differs from embodiment 1 in that, as the gas for finebubble in the water-softening treatment, not air but nitrogen is used inembodiment 2.

It is predicted that not only the actions of the aforementioned “(1)Metal Ion Adsorption” and “(2) Metal Ion Crystallization” but also theactions as described in the following sections (3) and (4) are enhancedby generating the fine nitrogen bubbles from the fine bubble generator3B to supply the bubbles into hard water. Note that the presentinvention is not necessarily restricted to the specific principledescribed in the following sections (3) and (4).

(3) Enhancement of Metal Ion Adsorption

As shown in FIG. 7(a), there are charged H⁺ and OH⁻ around the finebubble. As described above, the negatively charged OH⁻ adsorbs thepositively charged Ca²⁺. Under such a circumstance, when nitrogen isused for the fine bubble, the reaction of the following formula 3 isenhanced.

N₂+6H⁺+6e ⁻→2NH₃

NH₃+H₂O→NH₄ ⁺+OH⁻  (Formula 3)

Enhancement of the reaction of Formula 3 decreases the number of H⁺ ionsrelative to the number of OH⁻ ions, as shown in FIG. 7(b). Thereby, thenegative charge on the fine bubble becomes higher, and the positivelycharged Ca²⁺ becomes easy to adsorb.

In the case of using nitrogen as in embodiment 2, the reaction ofFormula 3 can be enhanced compared to the case of using air as inembodiment 1, and therefore the metal ion adsorption is furtherenhanced. Thereby, more metal ions can be separated and removed fromhard water.

The aforementioned principle is not limited to nitrogen, and possiblyany gas capable of reacting with H⁺ ions to reduce the number of H⁺ ionsrelative to the number of OH⁻ ions is also applicable.

(4) Enhancement of Metal Ion Crystallization

Since nitrogen is an inert gas different from air, once nitrogen issupplied into hard water, the partial pressure balance of the gascontained in hard water is lost. Thus, the reaction as shown in FIG. 8is enhanced.

As shown in FIG. 8, other gas components dissolved in hard water acts toreplace the fine bubble composed of nitrogen. In the example shown inFIG. 8, Ca(HCO₃)₂ present around the fine bubble contains CO₂, and thisCO₂ is extracted and acts to replace nitrogen. That is, the followingreaction is enhanced.

Ca(HCO₃)₂→CaCO₃+CO₂+H₂O  (Formula 4)

As described above, a reaction for generating insoluble CaCO₃ fromsoluble Ca(HCO₃)₂ is caused. At this time, CO₂ and H₂O are produced.Since CaCO₃ is insoluble, it precipitates as crystal of metal ion.

The above reaction makes it possible to crystallize and precipitate themetal ion contained as Ca²⁺ of Ca(HCO₃)₂ in hard water. Thereby, thecrystal of metal ion can be removed from hard water.

The aforementioned principle is not limited to nitrogen, and possiblyany gas other than air that loses the partial pressure balance of thegas dissolved in hard water is also applicable.

As described above, in embodiment 2, the reactions explained in thesections “(3) Enhancement of Metal Ion Adsorption” and “(4) Enhancementof Metal Ion Crystallization” can be enhanced compared to the case usingair by generating fine bubble incorporating nitrogen and supplying thefine bubble into hard water. Thereby, precision of the metal ion removalfrom hard water can be improved.

Embodiment 3

The metal ion removal method with the ion removal system according toembodiment 3 of the present invention will be explained. In embodiment3, primarily points different from points in embodiments 1 and 2 will beexplained, and descriptions overlapping the descriptions in embodiments1 and 2 are omitted.

Embodiment 3 defers from embodiments 1 and 2 in that the fine bubblegenerator 3B generates the fine bubble including air in embodiments 1and 2, whereas the fine bubble including a mixture gas of a plurality ofgases in embodiment 3.

In embodiment 3, a mixture gas of two gases, a first gas which is abasic gas and a second gas which has a slower solution velocity than ofthe first gas is used as a mixture gas for generating fine bubble. Thatis, the ion removal gas supplier 7 shown in FIG. 1 supplies the finebubble generator 3B with a mixture gas of the first gas and the secondgas as an ion removal gas.

It is predicted that not only the actions of the aforementioned “(1)Metal Ion Adsorption” and “(2) Metal Ion Crystallization” but also theactions as described in the following sections (5) and (6) are enhancedby generating the fine bubble with the mixture gas containing the firstgas and the second gas. Note that the present invention is notnecessarily restricted to the specific principle described in thefollowing sections (5) and (6).

(5) Potential Change on Fine Bubble Surface with First Gas

The first gas contained in the mixture gas is a basic gas which receivesH⁺ in an acid-base reaction. The first gas dissolves in water togenerate OH⁻. Specifically, a reaction of the following Formula 5-1 iscaused.

X+H₂O→XH⁺+OH⁻  (Formula 5-1)

In Formula 5-1, the first gas is represented by the chemical formula X.As a result of the reaction of Formula 5-1, a ratio of OH⁻ around a finebubble 40 increases compared to a ratio of H⁺ as shown in FIG. 9(illustration of H⁺ is omitted in FIG. 9). A potential of thesolid-liquid interface strongly depends on pH of the water qualitybecause H⁺/OH⁻ in water is a potential-determining ion. When H⁺increases, the positive charge becomes higher, and when OH⁻ increases,the negative charge becomes higher. Thereby, the negative charge on thefine bubble 40 becomes higher, and the positively charged Ca²⁺ becomeseasy to adsorb. In this manner, the effect of adsorbing the metal ionsto the fine bubble can be improved.

Furthermore, in embodiment 3, ammonia which is a basic gas is used asthe first gas. When using ammonia, the above Formula 5 is embodied inthe following Formula 6.

NH₃+H₂O→NH₄+OH⁻  (Formula 6)

As a result of generating the fine bubble 40 using ammonia which has ahigh aqueous solubility and is a general-purpose gas, a cost forgenerating the fine bubble 40 can be reduced while improving theaforementioned metal ion adsorption effect.

Incidentally, the aforementioned principle is not limited to ammonia,and possibly any basic gas is also applicable. Examples of such a basicgas include methylamine, ethylamine, propylamine, isopropylamine,butylamine, hexylamine, cyclohexylamine, dimethylamine, diethylamine,diisopropylamine, dipropylamine, di-n-butylamine, ethanolamine,diethylethanolamine, dimethylethanolamine, ethylenediamine,dimethylaminopropylamine, N,N-dimethylethylamine, trimethylamine,triethylamine, tetramethylenediamine, diethylenetriamine,propyleneimine, pentamethylenediamine, hexamethylenediamine, morpholine,N-methylmorpholine, and N-ethylmorpholine.

In addition, as shown in Formula 5-1, X is not limited to the basic gas,and it is considered that any “hydroxyl ion-donating gas” which reactswith water (H₂) to donate hydroxyl ion (OH⁻) exhibits the same effect.An example of the hydroxyl ion-donating gas is a soluble ozone gas (O₃).It is considered that when the ozone gas is supplied to water, areaction represented by the following Formula 5-2 similar to the aboveFormula 5-1 is caused.

O₃+H₂O+2e ⁻→O₂+2OH⁻  (Formula 5-2)

It is considered that, according to the above Formula 5-2, the hydroxylion-donating gas “X” capable of causing the reaction represented by thefollowing Formula 5-3 also exhibits the same effect.

XO+H₂O+2e ⁻→+X+2OH⁻  (Formula 5-3)

Ozone will be explained in Experimental example 6.

(6) Retention of Fine Bubble with Second Gas

As explained in the above section “(5) Potential Change on Fine BubbleSurface with First Gas”, the first gas as the basic gas contained in themixture gas dissolves in water to increase a ratio of OH⁻ on the surfaceof the fine bubble 40. Such a first gas is mixed with the second gashaving a slower solution velocity than of the first gas. As a result ofmixing such a second gas, the whole fine bubble 40 is prevented fromdissolving in water even when the first gas is dissolved in water, andthe state of the fine bubble 40 can be retained. The effect of adsorbingCa²⁺ ions resulting from the fine bubble explained in embodiments 1 and2 can be retained by retaining the state of the fine bubble 40.

In embodiment 3, nitrogen is used as the second gas. The fine bubble isgenerated using a general purpose gas nitrogen which is harmless tohuman bodies, so that a cost for generating the fine bubble 40 can bereduced while securing the safety. In addition, since nitrogen is anon-water soluble gas (non-soluble gas), the effect of maintaining thestate of the fine bubble 40 can be more effectively exhibited.

The aforementioned principle is not limited to nitrogen, and possiblyany gas having a slower solution velocity compared to that of the firstgas as the basic gas is also applicable. When the second gas isselected, a gas having a slower (lower) water solution velocity(solubility) than of the first gas under the same conditions includingthe temperature and the pressure may be selected. Examples of such asecond gas include, in ascending order of solubility, nitrogen,hydrogen, carbon monoxide, butane, oxygen, methane, propane, ethane,nitrogen monoxide, ethylene, propene, acetylene, and carbon dioxide.Above all, when the non-water soluble gas such as nitrogen monoxide,oxygen, and hydrogen is used, the effect of maintaining the state of thefine bubble 40 can be more effectively exhibited.

Incidentally, dissolution of nitrogen in hard water was explained wasexplained with reference to FIGS. 7 and 8 in the sections “(3)Enhancement of Metal Ion Adsorption” and “(4) Enhancement of Metal IonCrystallization”, and it is considered that these reactions are alsocaused at the same time. Nitrogen hardly dissolves in water because itis water-insoluble, and strongly exerts an action of retaining the stateof the fine bubble 40, but there is not a little water-soluble nitrogen.Thus, not a few phenomena of nitrogen dissolved in water as explained inthe sections “(3) Enhancement of Metal Ion Adsorption” and “(4)Enhancement of Metal Ion Crystallization” are considered to alsosimultaneously occur with the phenomena of nitrogen retaining the finebubble explained in the section “(6) Retention of Fine Bubble withSecond Gas”.

As described above, the fine bubble generator according to embodiment 3generates the fine bubble 40 with the mixture gas of the first gasconfigured to react with water to donate hydroxyl ions and the secondgas having a slower solution velocity compared to the first gas. Thefirst gas which is a hydroxyl ion-donating gas reacts with water toincrease the ratio of OH⁻ on the surface of the fine bubble 40. Thereby,the effect of adsorbing metal ions such as Ca²⁺ to the fine bubble 40can be increased. Furthermore, the second gas having a slower solutionvelocity compared to the first gas is mixed to prevent the fine bubble40 from completely dissolving in water and retain the state of the finebubble 40.

In embodiment 3, the first gas is a soluble basic gas (ammonia). In thismanner, the first gas as the basic gas is first dissolved in water, andthe second gas having a slower solution velocity compared to the basicgas is negatively charged, so that the aforementioned effect can beexhibited by utilizing the difference in the solution velocity betweentwo gases.

Although the mixing ratio of ammonia and nitrogen on the fine bubble 40may be set to any value, and for example, set so that a mixing ratio ofnitrogen to ammonia is high (e.g. a ratio (volume ratio) ofammonia:nitrogen is 1:99). As a result of such a setting, an area whereOH⁻ increases by dissolution of ammonia resides only as far as thevicinity of the surface of the fine bubble 40, and the OH ratio hardlychanges at a position away from the fine bubble 40. In this manner, thewater quality of the whole water can be prevented from changing whilechanging while changing only the vicinity of the surface of the finebubble 40. On the other hand, the state of the fine bubble 40 can bemaintained longer by increasing the ratio of nitrogen. In this manner,in the mixture gas, these effects can be exhibited by setting thequantity of the second gas having a slower solution velocity than of thebasic gas so as to be larger than the quantity of the first gas as thebasic gas. Note that, since the quantity is proportional to the volumeunder the same temperature and pressure conditions, either the quantityor the volume may be used to set the mixing ratio of the first gas andthe second gas.

Alternatively, the mixing ratio may be set so that the ratio of ammoniato nitrogen is high. As a result of such a setting, the metal ioncontained in hard water can be further crystallized and removed. Such aprinciple of crystallization enhancement will be explained inExperimental example 2-4.

Unlike the supplying configuration that ammonia and nitrogen areseparately formed into fine bubble and separately supplied to hard waterwithout mixing them, the fine bubble generator according to embodiment 3is intended to supply the fine bubble 40 with the mixture gas of ammoniaand nitrogen to hard water. According to such a supply method, ammoniais prevented from dissolving alone at a position away from the finebubble 40, and therefore a function of increasing OH⁻ only in thevicinity of the surface of the fine bubble 40 can be sufficientlyexhibited.

Next, the metal ion adsorbing effect of the fine bubble 40 with themixture gas of ammonia as the first gas and nitrogen as the second gas,particularly the hypothetical principle to finally crystallize the metalions will be explained with reference to the schematic drawing of FIG.10.

As shown in FIG. 10, once the fine bubble 40 is supplied into hardwater, the water-soluble ammonia out of ammonia and nitrogenconstituting the fine bubble 40 dissolves in the surrounding water(ammonia gas dissolution). Thereby, as explained in the section “(5)Potential Change on Fine Bubble Surface with First Gas”, NH₄ ⁺ isgenerated on the surface of the fine bubble 40 and the ratio of OH⁻increases (surface condensation). At this time, the Ca²⁺ ion adsorptioneffect increases.

As the surface condensation further progresses, the concentration of OHon the surface of the fine bubble 40 becomes maximum. That is, a pH onthe surface of the fine bubble 40 becomes maximum, and a zeta potentialof the fine bubble 40 becomes maximum (the local pH is high, and thezeta potential is high).

In the aforementioned states “ammonia gas dissolution”, “surfacecondensation”, and “high local pH and high zeta potential”, Ca²⁺ isadsorbed to the fine bubble 40. At this time, the fine bubble 40adsorbing Ca²⁺ can be separated from hard water to remove the metal ionsfrom hard water.

When the separation has not been carried out, or when the separation hasbeen carried out but some bubbles remain as the fine bubble 40, the Ca²⁺adsorbed to the surface of the fine bubble 40 starts to crystallize.Specifically, Ca²⁺ crystallizes and precipitates as a crystal 42.Furthermore, the fine bubble starts to disappear (disappearance) alongwith precipitation of the crystal 42.

As the crystallization of Ca²⁺ and the disappearance of the fine bubble40 progress, the non-water soluble nitrogen maintaining the state of thefine bubble diffuses as a dissolved gas into water (dissolved gasdiffusion).

In the aforementioned states “disappearance” and “dissolved gasdiffusion”, ions contained as metal ions in hard water precipitate asthe crystal 42. The crystal 42 precipitated in such a way can beseparated from hard water to crystallize and remove the metal ions inhard water.

Experimental Example 2-4

Next, Experimental example 2-4 will be explained for confirminginfluence of the mixing ratio of ammonia and nitrogen in the fine bubble40 on the metal component crystallization. The experiments were carriedout using a device 50 shown in FIG. 11.

FIG. 11 presents a schematic configuration of the device 50 used inExperimental example 2-4. The device 50 shown in FIG. 11 includes amixture gas supply section 52, a treatment tank 54, a first pipe 56, asecond pipe 58, a water collection valve 60, a water collector 62, and awater storage tank 64, a pump 66, a flow regulation valve 68, and aflowmeter 70.

The mixture gas supply section 52 refers to a member for supplying amixture gas to the treatment tank 54. The mixture gas supply section 52includes an ammonia supply source 72, a nitrogen supply source 74, amixing ratio regulation valve 76, a supply pipe 78, and a fine bubblegenerator 80.

The mixture gas supply section 52 generates a mixture gas, which isprepared by mixing ammonia (first gas) and nitrogen (second gas) usingthe ammonia supply source 72 and the nitrogen supply source 74. Themixing ratio of ammonia and nitrogen can be set to any ratio by themixing ratio regulation valve 76. The mixture gas is supplied to thefine bubble generator 80 disposed on the bottom portion of the treatmenttank 54 through the supply pipe 78. The fine bubble generator 80 refersto a member for forming the mixture gas into fine bubble.

The treatment tank 54 refers to a tank for storing hard water as waterto be treated (hard water storage section). Based on the principleexplained in embodiment 3, the metal components are removed,particularly crystallized from hard water by supplying fine bubble withthe mixture gas into hard water in the treatment tank 54. The treatedwater is sent to the first pipe 56. The water collection valve 60 isdisposed on the way of the first pipe 56. The treated water passingthrough the first pipe 56 is collected by opening and closing the watercollection valve 60. The collected treated water is put into the watercollector 62.

The first pipe 56 is connected to the water storage tank 64. The waterstorage tank 64 refers to a tank for storing the treated water. Thetreated water stored in the water storage tank 64 is returned to thetreatment tank 54 through the second pipe 58. Thereby, the treated watercirculates.

The second pipe 58 is equipped with the pump 66, the flow regulationvalve 68, and the flowmeter 70. The pump 66 refers to a member forgenerating a propulsive force for making the treated water in the waterstorage tank 64 flow through the second pipe 58. The flow regulationvalve 68 refers to a valve for regulating the flow rate of the treatedwater passing through the second pipe 58. The flowmeter 70 refers to anapparatus for measuring the flow rate of the treated water flowingthrough the second pipe 58.

Various parameters were measured in such a way that the metal componentsin hard water were removed in the treatment tank 54 while continuouslyoperating the pump 66 using this device 50, and the treated water wascollected from the water collector 62. In Experimental example 2-4, aratio of the crystallized metal components contained in the treatedwater (crystallization ratio) was investigated. Note that the“crystallization ratio” in the present specification means not only aratio of a crystal configured so that atoms and molecules areperiodically arranged with regularity but also a ratio of a meresubstance precipitated as a solid. The crystallization ratio may bereferred to as “precipitation ratio”.

FIG. 12 presents an example of a result of observing water actuallytreated in Experimental example 2-4 by a scanning electron microscope(SEM). As shown in FIG. 12, a lot of crystals 84 precipitate in atreated water 82.

In examples 2 and 3, a hard water 1 was used as water to be treated. Thehard water 1 is Evian (registered trademark) having a hardness of about300 mg/L. In Experimental example 4, two types of waters, the hard water1 and a hard water 2 were used. The hard water 2 is Contrex (registeredtrademark) having a hardness of about 1400 mg/L.

Experimental Example 2

In Experimental example 2, the treated water after a predetermined timehad elapsed was collected as a sample water by the water collector 62while flowing hard water into the treatment tank 54 by operating thepump 66 using the device 50. In Experimental example 2, the mixing ratioof ammonia and nitrogen in the mixture gas was varied to investigatedifference in the crystallization ratio at each mixing ratio. Specificexperimental conditions of Experimental example 2 will be describedbelow. In Experimental example 2, all the treated water supplied fromthe treatment tank 54 to the first pipe 56 was discarded except watercollected by the water collector 62, and was not supplied to waterstorage tank 64.

(Experimental Condition)

-   Type of water to be treated: Hard water 1-   Mixing ratio of ammonia in mixture gas: 0% (nitrogen only)    -   30%, 40%, 50%,    -   60%, 70%, 80%,    -   90%, 100% (ammonia only)-   Flow rate of water to be treated: 2.6 L/min-   Flow rate of mixture gas: 0.03 L/min-   Time from pump operation to collection: 3 minutes-   Measurement items of sample water: pH, Ca hardness (mg/L), total    carbonate concentration (mg/L)

The measurement items of the sample water were measured using water fromwhich crystal of metal component precipitated in the sample water wereremoved by filtering the collected sample water. The Ca hardness refersto a value obtained by converting the Ca²⁺ content in the treated waterper unit volume into calcium carbonate (CaCO₃). For measuring pH, Cahardness, and total carbonate concentration, each commercially availablemeasuring apparatus was used.

FIG. 13A and FIG. 13B present experimental results in Experimentalexample 2.

In FIG. 13A, the abscissa represents the mixing ratio (%) of ammonia inthe mixture gas, and the ordinate represents the crystallization ratio(%) of the sample water. In FIG. 13B, the abscissa represents the pH ofthe sample water, and the ordinate represents the crystallization ratio(%) of the sample water.

The “crystallization ratio” was calculated by an equation (Ca hardnessof sample water before operation—Ca hardness of sample water afteroperation)/Ca hardness of sample water before operation. Thecrystallization ratio calculated in such a way expresses how much metalion has crystallized per unit volume of the sample water. The highercrystallization ratio expresses that more metal ion is crystallized fromthe sample water.

FIGS. 13A and 13B show that the higher the mixing ratio of ammonia is,the higher the crystallization ratio is. In particular, when the mixingratio of ammonia is 70% or higher, the crystallization ratiodramatically increases.

FIGS. 13A and 13B show that the higher the mixing ratio of ammonia is,the higher the pH is. However, although the pH increases, the valueshifts between at most 8.5 and 9. The pH reference value of tap waterdefined by the Ministry of Health, Labor and Welfare ranges 5.8 to 8.6,and it can be seen that even when the mixing ratio of ammonia is high,the pH value shifts in a range close to the range of the tap water. Adesirable pH range of alkaline ionized water for drinking defined in Acton Securing Quality, Efficacy and Safety of Products IncludingPharmaceuticals and Medical Devices is pH 9 to 10. Since the pH valuecan be suppressed lower than this range, the sample water is proved tobe suitable also as drinking water.

It is considered that the reason why increase in pH does not excessivelyrise even when the mixing ratio of ammonia is high is because not the pHof the whole treated water but rather the pH at the local area aroundthe fine bubble 40 is primarily raised, as explained with reference toFIG. 10.

Experimental Example 3

In Experimental example 3, like Experimental example 2, the treatedwater after a predetermined time had elapsed was collected as a samplewater by the water collector 62 while flowing hard water into thetreatment tank 54 by operating the pump 66 using the device 50. InExperimental example 3, only two patterns of ammonia mixing ratios 70%and 100% in the mixture gas were used. In addition, unlike Experimentalexample 2, the sample water was collected at predetermined intervalsfrom the operation of the pump 66 to measure various parameters.Furthermore, unlike Experimental example 2, all the treated watersupplied from the treatment tank 54 to the first pipe 56 was returned tothe water storage tank 64 except water collected by the water collector62, and was circulated. Specific experimental conditions of Experimentalexample 3 will be described below.

(Experimental Condition)

-   Type of water to be treated: Hard water 1-   Mixing ratio of ammonia in mixture gas: 70%, 100% (only ammonia)-   Flow rate of water to be treated: 2.6 L/min-   Flow rate of mixture gas: 0.03 L/min-   Measurement items of sample water: pH, Ca hardness (mg/L), total    carbonate concentration (mg/L)

FIG. 14A, FIG. 14B, and FIG. 14C present experimental results inExperimental example 3.

In FIG. 14A, the abscissa represents the operation time (minute) of thepump 66, and the ordinate represents the crystallization ratio (%) ofthe sample water. In FIG. 14B, the abscissa represents the operationtime (minute) of the pump 66, and the ordinate represents the Cahardness (mg/L) of the sample water. In FIG. 14C, the abscissarepresents the operation time (minute) of the pump 66, and the ordinaterepresents the pH of the sample water.

As shown in FIG. 14A, in both cases of the ammonia mixing ratios of 70%and 100%, the crystallization ratio increases as the operation timepasses. In addition, the Ca hardness decreases as the operation timepasses, as shown in FIG. 14B. This reveals that Ca²⁺ of the metalcomponents dissolved in hard water is crystallized as CaCO₃ byintroducing the fine bubble with the mixture gas.

On the other hand, in the case of the ammonia mixing ratio of 100%rather than the case of 70%, the increasing rate of the crystallizationratio and the decreasing rate of the Ca hardness are enhanced. Thisreveals that ammonia significantly contributes to the crystallization ofCa²⁺ into CaCO³.

As shown in FIG. 14C, in both cases of the ammonia mixing ratios of 70%and 100%, the pH loosely increases as the operation time passes. Thereis not so significant difference in the pH between the cases of theammonia mixing ratios of 70% and 100%. Also, even after 50 minutes haspassed from the start of the operation, the pH is between 9 and 10 anddoes not excessively increases. It is considered that the reason why theincreasing rate of the pH does not so excessively increase as describedabove is because not the pH of the whole treated water but rather the pHat the local area around the fine bubble 40 is primarily raised, asexplained with reference to FIG. 10.

Experimental Example 4

In Experimental example 4, like examples 2 and 3, the treated waterafter a predetermined time had elapsed was collected as a sample waterby the water collector 62 while flowing hard water into the treatmenttank 54 by operating the pump 66 using the device 50. In the same manneras in Experimental example 3, the sample water was collected atpredetermined intervals from the operation of the pump 66 to measurevarious parameters. In the same manner as in Experimental example 3, allthe treated water supplied from the treatment tank 54 to the first pipe56 was returned to the water storage tank 64 except water collected bythe water collector 62, and was circulated. On the other hand, inExperimental example 4, only one pattern of ammonia mixing ratio 70% inthe mixture gas was used. In addition, unlike examples 2 and 3, twotypes of hard water, hard water 1 (hardness: about 300 mg/L) and hardwater 2 (hardness: about 1400 mg/L) were used as the treated water.Specific experimental conditions of Experimental example 4 will bedescribed below.

(Experimental Condition)

-   Type of water to be treated: Hard water 1 and hard water 2-   Mixing ratio of ammonia in mixture gas: 70%-   Flow rate of water to be treated: 2.6 L/min-   Flow rate of mixture gas: 0.03 L/min-   Measurement items of sample water: pH, Ca hardness (mg/L), total    carbonate concentration (mg/L)

FIG. 15A, FIG. 15B, FIG. 15C, and FIG. 15D present experimental resultsin Experimental example 4.

In FIG. 15A, the abscissa represents the operation time (minute) of thepump 66, and the ordinate represents the crystallization ratio (%) ofthe sample water. In FIG. 15B, the abscissa represents the operationtime (minute) of the pump 66, and the ordinate represents the Cahardness (mg/L) of the sample water. In FIG. 15C, the abscissarepresents the operation time (minute) of the pump 66, and the ordinaterepresents the pH of the sample water. FIG. 15D presents a graph ofwhich the ordinate is added with the total carbonate concentration(mg/L) in the graph of FIG. 15B.

As shown in FIGS. 15A and 15B, in both the hard water 1 and the hardwater 2, the crystallization ratio increases and the Ca hardnessdecreases as the operation time passes. This reveals that Ca²⁺ of themetal components dissolved in hard water is crystallized as CaCO₃ byintroducing the fine bubble with the mixture gas.

In addition, FIGS. 15A and 15C show that there are significantdifferences in the increasing rates of the crystallization ratio and thepH between the hard water 1 and the hard water 2. Specifically, it canbe seen that the hard water 1 has higher increasing rates of thecrystallization ratio and the pH than those of the hard water 2. In thisregard, the inventors of the present invention focused on the “totalcarbonate concentration” and examined the “total carbonateconcentration” based on the data shown in FIG. 15D.

As shown in FIG. 15D, a value of the total carbonate concentration inthe hard water 1 is 150 to 200 mg/L when the operation time is 50minutes. That is, the hard water 1 contains large amounts of HCO₃ ⁻ andCO₃ ²⁻. When the operation time is 50 minutes, the crystallization ratioof the hard water 1 reaches 70 to 80% as shown in FIG. 15A. On the otherhand, a value of the total carbonate concentration in the hard water 2is about 20 mg/L when the operation time is 70 minutes. Comparison withhard water 1 shows that the hard water 2 has considerably small amountsof HCO₃ ⁻ and CO₃ ²⁻. Incidentally, when the operation time is 70minutes, the crystallization ratio of the hard water 2 is expected to beabout 40% according to the data in FIG. 15A.

HCO₃ ⁻ and CO₃ ²⁻ function as components for crystallizing as Ca²⁺ asCaCO₃, as explained for the principles of embodiments 1 to 3. Since thehard water 1 contains large amounts of HCO₃ ⁻ and CO₃ ²⁻, the hard water1 is considered to have a higher increasing rate of the crystallizationratio than of the hard water 2.

The metal component content and the total carbonate concentrations inthe hard waters 1 and 2 are shown in the following Table 1.

TABLE 1 CO₃ ²⁻ content required Surplus Content (mg/L) for dissolution(mg/L) amount Ca Mg CO₃ ²⁻ Ca Mg Total (mg/L) Molecular weight 40 24.360 60 Contrex 468 74.8 372 702 184.691358 886.691358 −514.691 Evian 8026 357 120 64.19753086 184.1975309 172.8025

As shown in Table 1, in Evian (registered trademark) as the hard water1, the contents of Ca, Mg and CO₃ ²⁻ per unit volume of Evian are 80,26, and 357 mg/L respectively. In Contrex (registered trademark) as thehard water 2, the contents of Ca, Mg and CO₃ ²⁻ per unit volume ofContrex are 468, 74.8, and 372 mg/L respectively. As described above, inthe hard water 1 and hard water 2, the CO₃ ²⁻ contents per unit volumesare 357 mg/L and 372 mg/L respectively, which are approximately equal toeach other. On the other hand, the CO₃ ²⁻ content required fordissolving Ca and Mg relative to the Ca and Mg content in hard water isabout 184 mg/L in the hard water 1, and about 887 mg/L in the hard water2. That is, in the hard water 1, the amount of the actually containedCO₃ ²⁻ is in excessive by about 173 mg/L relative to the CO₃ ²⁻ contentrequired for dissolving Ca and Mg. This means that when introducing themixture gas with the fine bubble, there is a plenty of CO₃ ²⁻ forcrystallizing Ca²⁺. On the other hand, in the hard water 2, the amountof the actually contained CO₃ ²⁻ is in shortage by about 515 mg/Lrelative to the CO₃ ²⁻ content required for dissolving Ca and Mg. Thismeans that when introducing the mixture gas with the fine bubble, thereis a small amount of CO₃ ²⁻ for crystallizing Ca²⁺, and thecrystallization is not enhanced.

From the above results, it is considered that when the hard water to betreated contains a plenty of carbonates such as HCO₃ and CO₃ ²⁻, theincreasing rate of the crystallization can be improved. For the purposeof increasing the total carbonate content in hard water based on thisresult, carbon dioxide gas may be introduced into hard water before thefine bubble is introduced. Specifically, a carbon dioxide gas generatorfor generating carbon dioxide gas may be further installed. In addition,carbon dioxide gas may be generated by the carbon dioxide gas generatorand supplied to hard water before supplying the fine bubble generated bythe fine bubble generator to hard water. It is considered that thisprocess can enhance crystallization of the metal components in hardwater.

As described above, according to Experimental example 2-4,crystallization of the metal components can be enhanced by setting thequantity of ammonia so as to be larger than the quantity of nitrogen inthe mixture gas. Furthermore, crystallization of the metal componentscan be greatly enhanced by setting the mixing ratio of ammonia in themixture gas to 70% or higher.

Experimental Example 5

Experimental example 5 includes a sensory evaluation experiment forevaluating “foaming” for the sample water (soft water) treated using theaforementioned device 50. The foaming is related to the foaming powerdepending on heights and sizes of the foam generated from the watersurface. It is generally supposed that the smaller the amount of thehardness components is, the larger the foaming is, e.g. providing suchan advantage that a washing effect is enhanced when the water is usedfor the purpose of washing.

In Experimental example 5, unlike Experimental example 2-4, fine bubblewere produced originating from a single gas ammonia instead of themixture gas. That is, in the device 50 shown in FIG. 11, fine bubblewere produced using only an ammonia supply source 72 without using thenitrogen supply source 74. Since the method of using the device 50 isthe same as in Experimental example 2-4, explanation of the method isomitted.

The experimental method of Experimental example 5 is based on thestandard of “foaming”: SHASE-S 218 of Society of Heating,Air-conditioning and Sanitary Engineers of Japan. Specifically, dilutedwater was prepared by diluting 1.5 g of pure soap with 200 ml of water,then 1 mL of the diluted water and 9 mL of water to be treated weremixed, and 10 mL of the mixture as an evaluation water was put into ameasuring cylinder. As the pure soap, Cow brand red box a1 toilet soap(Cow Brand Soap Kyoshinsha Co., Ltd.) was used, and as 200 ml of water,distilled waterAutostil WG221 (Yamato Scientific co., ltd.) was used.The measuring cylinder was shaken 50 times, and after 1 minute, a heightof the foam from the water surface was measured.

In Experimental example 5, the same experiment was performed using, inaddition to the sample water treated by the device 50, three types ofwater, hard water, tap water, and pure water. Hardnesses of these watersand the sample water are as follows.

-   Hardness of hard water: Overall hardness is 300 mg/L, Ca hardness is    200 mg/L, Mg hardness is 100 mg/L-   Hardness of tap water: Overall hardness is 72 mg/L, Ca hardness is    49 mg/L, Mg hardness is 23 mg/L-   Hardness of pure water: Overall hardness is 0 mg/L, Ca hardness is 0    mg/L, Mg hardness is 0 mg/L-   Hardness of sample water: Overall hardness is 118 mg/L, Ca hardness    is 21 mg/L, Mg hardness is 97 mg/L

FIG. 16 presents experimental results in Experimental example 5. In FIG.16, the abscissa represents the type of water, and the ordinaterepresents the height (mm) of the foam extending from the surface of theevaluation water. The ordinate represents foaming and foaming power.

As shown in FIG. 16, the “hard water” which was highest in both the Caand Mg hardnesses showed almost no foaming and the hardnesses were closeto 0, whereas the “tap water”, “sample water” and “pure water” showedalmost the same high foaming levels. That is, in the “sample water”treated using the device 50, the foaming is improved relative to thehard water before treatment and achieves foaming close to those of “tapwater” and “pure water”. This revealed that foaming could be improved byremoving the metal ions from hard water using the method in embodiments,and foaming at the same level as of tap water and pure water as softwater could be achieved.

When comparing the results shown in FIG. 16 with the concrete values ofthe hardness, the lower the Ca hardness is, the higher the foaming levelis. This reveals that the Mg hardness value rather than the Ca hardnessvalue is a dominant parameter that directly affects foaming.

Experimental Example 6

In embodiment 6, the water to be treated (hard water) is treated usingthe same device 50 (FIG. 11) as in Experimental example 2-4, and thetreated sample waters are compared for the crystallization ratio.

In Experimental example 6, the difference in the crystallization ratiowas examined by comparing the crystallization ratios between the caseusing micro-bubbles as fine bubble and the case of using milli-bubblesas non-fine bubble. That is, in the device 50 shown in FIG. 11, anexperiment was carried out in two patterns, a pattern using the finebubble generation section 80 as it is to generate micro-bubbles, and apattern using another bubble generation section (not shown) instead ofthe fine bubble generation section 80 to generate milli-bubbles.

In Experimental example 6, unlike Experimental example 2-4, furthermorebubbles were produced originating from a single gas ozone instead of themixture gas. That is, in the device 50 shown in FIG. 11, an ozone supplysource (not shown) was used instead of the ammonia supply source 72 andthe nitrogen supply source 74. As explained in embodiment 3, the ozonegas is a hydroxyl ion-donating gas.

The experimental conditions of Experimental example 6 are as follows.

-   Type of water to be treated (common): Hard water 1-   Flow rate of water to be treated (common): 12 L/min-   Volume of water stored in the treatment tank 54 9 L (common):-   Flow rate of ozone gas (common): 0.12 L/min-   Average diameter of micro-bubbles: 56 μm-   Average diameter of milli-bubbles: 1021 μm-   Measurement items of sample water (common): Ca hardness (mg/L),    overall hardness (mg/L)

FIG. 17A and FIG. 17B present experimental results in Experimentalexample 6.

In FIG. 17A, the abscissa represents time (minute), and the ordinaterepresents the crystallization ratio (%) of the Ca hardness. In FIG.178, the abscissa represents time (minute), and the ordinate representsthe crystallization ratio (%) of the overall hardness.

FIG. 17A and FIG. 17B reveal that both the Ca hardness and the overallhardness of the micro-bubbles achieve higher crystallization ratios thanof the milli-bubbles. That is, it was demonstrated that the case usingthe micro-bubbles as fine bubble had a higher crystallization ratio thanthose in the case using the milli-bubbles as non-fine bubble, achievingthe metal ion crystallization effect with fine bubble.

Not limited to the above-mentioned embodiments, the present inventioncan be implemented in various other modes. For example, although themetal ion is Ca²⁺ and the particle is CaCO₃ in the above explanation,the present invention is not limited to such a case. When the metal ionis Ca²⁺, the particle may be, not limited to CaCO₃, any particlecontaining Ca as a constituent element (e.g., calcium phosphate(Ca₃(PO₄)₂)). Furthermore, the metal ion is not limited to Ca²⁺, and maybe another metal ion (e.g., Mg²⁺ or other Group 2 element).

In the above explanation, the particle feeder 102 is connected to thefeeding points 108A, 110A, and 112A via the three flow paths 108, 110,and 112, respectively, but not limited thereto, the particle feeder 102may be connected to other feeding point. If a feeding point is setupstream of the hard water storage 3A in the hard water flow directionor in the hard water storage 3A, the same effects as in embodiment 1 canbe exhibited.

Furthermore, in the above explanation, the three flow paths 108, 110,and 112 and the three feeding points 108A, 110A, and 112A are provided,but not limited thereto, one of the flow paths and one of the feedingpoints may only be provided.

The particle feeder 102 includes the particle feeding mechanism 104 andthe particle storage 106 in the above explanation, but the presentinvention is not limited thereto. For example, a particle feeder 202 asshown in FIG. 18 may be used. In an ion removal system 200 shown in FIG.18, the particle feeder 202 itself is a device configured to generate aparticle. Specifically, the particle feeder 202 is a reaction tankconfigured to causes a reaction to generate a particle. In such a case,a reaction using phosphoric acid, sodium hydrogen carbonate and the likeas a raw material may be caused as shown in the following equation 7.

5Ca²⁺+3HPO₄ ²⁻+4OH⁻→Cas(OH)(PO₄)₃↓+3H₂O

CaCL₂+2NaHCO₃→CaCO₃↓+2NaCl+H₂OCO₂↑  (Equation 7)

According to the embodiment shown in FIG. 18, the particle feeder 202can have a simple configuration.

In the above description, air or nitrogen is used as the ion removal gasin the water-softening treatment, but the present invention is notlimited thereto. A gas other than air and nitrogen may be used as theion removal gas.

Furthermore, in the above explanation, carbon dioxide is used as thedissolving gas for performing the reproduction treatment, but thepresent invention is not limited thereto. For example, hydrogen sulfide(H₂S→H⁺+HS⁻) or hydrogen chloride (HCL→H⁺+CL⁻), which is a gas toproduce a hydrogen ion when dissolved in water, may be used as thedissolving gas.

Furthermore, in the above description, the dissolving gas is used as anexample of the dissolving agent for performing the reproductiontreatment, but the present invention is not limited thereto. Forexample, a liquid (that is, “dissolving liquid”) configured to dissolvethe crystal of metal component may be used as the dissolving agent.Examples of such a liquid include hydrochloric acid, sulfuric acid,citric acid, and ascorbic acid. Using such a liquid can reduce the sizeof the dissolving agent supplier 8. Furthermore, the frequency ofexchanging the dissolving agent can be reduced. When a liquid is used asthe dissolving agent, it is possible to prevent gas from entering thepump P, thereby eliminating the need for disposing the dissolving agentsupplier 8 downstream of the pump P in the flow direction of the hardwater. That is, the dissolving agent supplier 8 may be disposed in thecirculation flow path constituted by the primary flow path 2, the ionremoval device 3, the separation device 4, and the return flow path 12.With this configuration, the dissolving agent can also be supplied tothe separation device 4 to dissolve the crystal adhering to theseparation device 4 for the reproduction treatment.

Furthermore, in the above description, only the fine bubble containingthe ion removal gas is supplied into the hard water, but the presentinvention is not limited thereto. For example, other gas may be suppliedinto the hard water in addition to the fine bubble containing the ionremoval gas. In this case, the other gas may be supplied to the hardwater as a fine bubble or may be supplied to the hard water as a normalbubble.

Furthermore, in the above description, the opening/closing operations ofthe first valve 15A, the second valve 15B, and the third valve 15C areautomatically controlled by the control unit 6, but the presentinvention is not limited thereto. The opening/closing operations of thefirst valve 15A, the second valve 15B, and the third valve 15 c may beperformed manually.

Additionally, in the above description, the fine bubble including themixed two gases with the first gas as a basic gas and the second gashaving a slower solution velocity than the first gas is used, other gasmay be mixed in addition to these two gases. That is, a fine bubble witha mixed gas of two or more types of gases including the first and secondgases may be used.

Incidentally, among the various embodiments and variations, anyembodiments can be appropriately combined to exhibit each effect of eachembodiment.

The present disclosure has been sufficiently described in connectionwith the preferable embodiments with reference to the appended drawings,but various variations and modifications are obvious to those skilled inthe art. Such variations and modifications should be understood asincluded within the scope of the present disclosure according to theappended claims without departing from the scope. In addition, changesin the combination or the order of the elements in each embodiment canbe achieved without departing from the scope and the spirit of thepresent disclosure.

INDUSTRIAL APPLICABILITY

Since the ion removal system according to the present invention hasbetter maintainability and environmental property, it is useful for bothan ion removal system for home and an ion removal system for business.

DESCRIPTION OF REFERENCE SIGNS

-   -   1 Ion removal system    -   2 Primary flow path    -   3 Ion removal device    -   3A Hard water storage    -   3B Fine bubble generator    -   3C Connection flow path    -   4 Separation device    -   4A Separation section    -   4Aa Inner peripheral surface    -   4B Crystal storage    -   4Ba Discharge flow path    -   5 Secondary flow path    -   6 Control unit    -   7 Ion removal gas supplier    -   8 Dissolving agent supplier    -   9 Gas switching mechanism    -   10 Opening/closing valve    -   11 Discharging-side backflow prevention mechanism    -   12 Return flow path    -   13 Supply-side backflow prevention mechanism    -   14 Bypass flow path    -   15A First valve    -   15B Second valve    -   15C Third valve    -   20 Device    -   21 Hard water    -   22 Water tank    -   22 a Bottom surface    -   22 b Water surface    -   24 Gas supplier    -   25 First pipe    -   26 Fine bubble generator    -   27 Second pipe    -   28 Pump    -   30 First water intake section    -   32 Second water intake section    -   34 Metal ion concentration detector    -   40 Fine bubble    -   42 Crystal    -   D1 Distance from first water intake section to second water        intake section    -   50 Device    -   52 Mixed gas supplier    -   54 Treatment tank    -   56 First pipe    -   58 Second pipe    -   60 Water collection valve    -   62 Water collector    -   64 Water storage tank    -   66 Pump    -   68 Flow regulation valve    -   70 Flowmeter    -   72 Ammonia supply source    -   74 Nitrogen supply source    -   76 Mixing ratio regulation valve    -   78 Supply pipe    -   80 Fine bubble generator    -   82 Treated water    -   84 Crystal    -   100 Ion removal gas storage    -   102 Particle feeder    -   104 Particle feeding mechanism    -   106 Particle storage    -   108 First flow path    -   108A First feeding point    -   110 Second flow path    -   110A Second feeding point    -   112 Third flow path    -   112A Third feeding point    -   120 Ion removal gas flow path    -   122 Dissolving agent flow path    -   200 Ion removal system    -   202 Particle feeder (reaction tank)

1. An ion removal system comprising: an ion removal device including ahard water storage configured to store hard water and a fine bubblegenerator configured to generate a fine bubble to supply the hard waterstorage with the fine bubble, for removing a metal ion from the hardwater by adsorbing the metal ion in the hard water to the fines bubblein the hard water storage and crystallizing and precipitating theadsorbed metal ion; and a particle feeder configured to bring a particlecontaining a same element as that of the metal ion into the hard waterat a feeding point, the feeding point being located upstream of the hardwater storage or located in the hard water storage.
 2. The ion removalsystem according to claim 1, wherein the metal ion is a calcium ion; andthe particle is calcium carbonate.
 3. The ion removal system accordingto claim 1, wherein the particle feeder includes: a particle feedingmechanism connected to the feeding point to bring the particle to thefeeding point; and a particle storage configured to store the particleto be supplied to the particle feeding mechanism.
 4. The ion removalsystem according to claim 3, further comprising an ion removal gasstorage configured to store an ion removal gas as a raw material of thefine bubble generated by the fine bubble generator, wherein the particlestorage and the ion removal gas storage are integrated with each other.5. The ion removal system according to claim 1, comprising: an ionremoval gas supplier configured to supply the fine bubble generator withan ion removal gas as a raw material of the fine bubble generated by thefine bubble generator; and an ion removal gas flow path connecting theion removal gas supplier and the fine bubble generator with each other,wherein the feeding point is located in the ion removal gas flow path.6. The ion removal system according to claim 1, further comprising aprimary flow path for supplying the ion removal device with the hardwater, wherein the feeding point is located in the primary flow path. 7.The ion removal system according to claim 1, wherein the feeding pointis located in the hard water storage.
 8. The ion removal systemaccording to claim 1, wherein the particle feeder brings the gelparticle.
 9. The ion removal system according to claim 2, wherein theparticle feeder includes: a particle feeding mechanism connected to thefeeding point to bring the particle to the feeding point; and a particlestorage configured to store the particle to be supplied to the particlefeeding mechanism.
 10. The ion removal system according to claim 9,further comprising an ion removal gas storage configured to store an ionremoval gas as a raw material of the fine bubble generated by the finebubble generator, wherein the particle storage and the ion removal gasstorage are integrated with each other.
 11. The ion removal systemaccording to claim 2, comprising: an ion removal gas supplier configuredto supply the fine bubble generator with an ion removal gas as a rawmaterial of the fine bubble generated by the fine bubble generator; andan ion removal gas flow path connecting the ion removal gas supplier andthe fine bubble generator with each other, wherein the feeding point islocated in the ion removal gas flow path.
 12. The ion removal systemaccording to claim 2, further comprising a primary flow path forsupplying the ion removal device with the hard water, wherein thefeeding point is located in the primary flow path.
 13. The ion removalsystem according to claim 2, wherein the feeding point is located in thehard water storage.
 14. The ion removal system according to claim 2wherein the particle feeder brings the gel particle.